LRU

the set_lru_capacity method can be used to fix the maximum capacity for a query at a specific number of values. If more values are added after that point, then salsa will drop the values from older memos to conserve memory (we always retain the dependency information for those memos, however, so that we can still compute whether values may have changed, even if we don't know what that value is). The LRU mechanism was introduced in RFC #4.